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Pnicogen-bonded complexes H(n)F(5-n)P:N-base, for n = 0-5
Janet E Del Bene1, Ibon Alkorta, José Elguero
1Department of Chemistry, Youngstown State University , Youngstown, Ohio 44555, United States.
The Journal of Physical Chemistry. A
|October 21, 2014
Summary
This study explores pnicogen-bonded complexes using ab initio calculations, revealing that equatorial fluorine atoms and axial alignment significantly influence interaction energies and structures. Base electron-donating ability also plays a key role.
Area of Science:
- Computational Chemistry
- Quantum Chemistry
- Supramolecular Chemistry
Background:
- Pnicogen bonding is an important non-covalent interaction involving Group 15 elements.
- Understanding the factors governing the structure and stability of pnicogen-bonded complexes is crucial for predicting their properties.
- Previous studies have explored various aspects of pnicogen bonding, but a systematic investigation of fluorine-substituted phosphorus acids is lacking.
Purpose of the Study:
- To investigate the structures and interaction energies of pnicogen-bonded complexes formed between fluorine-substituted phosphorus acids (H(n)F(5-n)P) and various nitrogen bases.
- To elucidate the factors influencing the geometries and binding strengths, including the role of equatorial fluorine atoms and axial alignment.
- To analyze the charge transfer characteristics and spin-spin coupling constants within these complexes.
Main Methods:
- Ab initio MP2/aug'-cc-pVTZ calculations were employed to model the electronic structure and properties of the complexes.
- Geometries were optimized, and interaction energies were computed for a series of pnicogen-bonded complexes.
- Analysis included bond distances, bond angles, charge transfer, and spin-spin coupling constants.
Main Results:
- Complex structures exhibited C(4v) or C(2v) symmetry, with P-N distances and interaction energies varying significantly.
- The F(ax)-P-F(eq) angle was found to correlate with P-N distances and approach values seen in Berry pseudorotation.
- Interaction energies decreased in the order NC(-) > NCLi > NP > NCH > NCF for a fixed acid, with equatorial fluorine count and axial alignment being dominant factors.
- Charge transfer from the nitrogen lone pair to the σ* P-A(ax) orbital was identified as a key stabilizing factor, correlating with interaction energies.
- Spin-spin coupling constants ((1p)J(P-N), (1)J(P-F(ax)), (1)J(P-H(ax))) showed distinct patterns and correlations with distances.
Conclusions:
- The number of equatorial fluorine atoms and the linearity of the axial P···N or P···H alignment are critical determinants of pnicogen-bonded complex structures and energies.
- The electron-donating ability of the nitrogen base significantly influences the complex's stability.
- Charge transfer plays a crucial role in stabilizing these complexes, and spin-spin coupling constants provide valuable insights into bonding characteristics.
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